(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to prepare the surface of a semiconductor substrate for subsequent processing sequences.
(2) Description of Prior Art
Micro-miniaturization, or the ability to fabricate semiconductor devices comprised with sub-micron features, have allowed the semiconductor industry to improve device performance while still decreasing fabrication costs. The use of smaller active device regions allow performance degrading parasitic capacitances to be reduced, while the use of smaller features result in a greater number of smaller semiconductor clips to be obtained from a specific size starting substrate, thus reducing the processing cost of a specific semiconductor chip. However the advent of micro-miniaturization can place more stringent demands on specific semiconductor processes, such as the ability to grow a thin gate insulator layers (silicon dioxide, silicon oxynitride, high k dielectrics, etc). With the arrival of micro-miniaturization metal oxide semiconductor (MOS), complimentary MOS (CMOS), and bipolarxe2x80x94CMOS (BiCMOS), devices are designed to operate at low voltages, thus necessitating the growth of a gate insulator layer comprised at a thickness of less than 100 Angstroms. The ability to thermally grow insulator layers (silicon dioxide, silicon oxynitride, high k dielectrics, etc), at these thicknesses, less than 100 Angstroms, demands ultra-clean, starting silicon surfaces. Therefore small amounts of metallic impurities residing on the silicon surface, which may not have deleteriously influenced the ability to thermally grow a thicker, high integrity silicon dioxide layer, now for thinner silicon dioxide layers can interfere with the attainment of a high quality, silicon dioxide layer.
This invention will teach a novel process sequence for preparing the surface of a semiconductor substrate for subsequent semiconductor procedures, such as the growth of a thin silicon dioxide gate insulator layer, or the formation of a metal silicide layer. This invention will describe the chemistry needed to achieve the desired surface, as well as presenting a surface preparation procedure with reduced process time, when compared to counterpart surface preparation procedures, thus reducing processing costs. Prior art, such as Kaji et al, in U.S. Pat. No. 5,650,043, Konuma et al, in U.S. Pat. No. 5,976,988, and Tsuji, in U.S. Pat. No. 5,454,901, describe procedures for cleaning a semiconductor surface prior to a subsequent process step. These prior arts however do not describe the unique chemistry described in the present invention, in which a greater level of metallic impurities are removed from a semiconductor surface, in a shorter period of time, when compared to counterpart processes which do not remove comparable levels of metallic impurities while however still requiring longer clean times.
It is an object of this invention to provide a method of preparing a semiconductor surface for subsequent processing steps via removal of metallic impurities, and etching of the exposed semiconductor substrate using a wet chemical clean procedure featuring NH4F and HCl as major components of the wet chemical solution.
It is another object of this invention to reduce the cost of, and to minimize the process time for, the wet chemical clean procedure employed to prepare a semiconductor substrate for subsequent processing steps.
In accordance with the present invention a method of preparing the surface of a semiconductor substrate for subsequent processing steps, in regards to removal of metallic impurities from a semiconductor substrate, via use of a wet chemical clean procedure, is described. A semiconductor substrate, being prepared for a silicon dioxide gate insulator layer, thermal oxidation procedure, is first subjected to a H2SO4:H2O2 solution to remove organic contamination from, and to grow a native oxide on, the exposed semiconductor substrate. An NH4F:HCl:H2O solution is then used to remove native oxide and desorb metallic impurities from the semiconductor surface. A drying cycle using iso-propyl alcohol (IPA), concludes the wet clean procedure. The wet clean procedure is also used to prepare surfaces prior to metal silicide formation, as well to remove organic contaminants, as well as metallic impurities, after such process steps as chemical mechanical polishing, and photoresist removal.